1. Field of the Invention
The present invention relates to adventitious citrus juice vesicles having the unique characteristic that they branch out of pre-existing citrus juice vesicles cultured in vitro.
2. Description of the Art
The citrus fruit is unique among the angiosperms. The fruit is a berry (hesperidium) consisting of 6-20 united carpels. These carpels are oriented vertically with their margins curved adaxially to join the floral axis thus forming locules. Exterior to the locules is the pericarp which is subdivided into three regions. The exocarp or flavedo (exterior peel) consists of the outermost layers of the fruit. The endocarp is the inner portion of the pericarp and a portion of the locular membrane. The mesocarp or albedo occurs between the exocarp and endocarp (H. Schneider, Chapter 1, "The Anatomy of Citrus," in The Citrus Industry, Vol. II, Eds. W. Reuther et al., University of California Press, pp. 1-85, 1968).
Citrus juice vesicles are an organized, specialized group of cells which accumulate juice. In nature, they arise from primordial bumps on the surface of the citrus endocarp and grow from the endocarp into the locules where they compactly fill the locules. Through cell division they differentiate into elliptical-shaped juice vesicles consisting of a distinct stalk and a single terminal body with tapered ends. They are characterized as being uniform solitary stalked structures. The mature vesicles are saclike in nature; the exterior skin encloses large vacuolated cells containing the materials which make up the juice. Juice vesicle cells are unique in terms of fruit anatomy. In these cells, the vacuole is very large, almost completely filling the interior of the cell.
Citrus juice vesicles make up the edible portion of the citrus fruit, and therefore they are of great economic value. The conventional method of producing edible citrus tissue, i.e., juice vesicles, has been to establish citrus trees in soil, cultivate them for years and then once they fruit, harvest the citrus fruit. The edible endocarp tissue is consumed either as fresh fruit or is processed to produce citrus juice. This method of producing fruit and endocarp tissue has several drawbacks. It requires much land for citrus fruit cultivation and is very labor intensive. Further, in usual husbandry practices, the fruit is periodically exposed pesticides and herbicides which have the potential for harm to man, beneficial insects, and the environment.
Various investigators have reported research on in vitro culture of citrus vesicles or explants. Production of new juice vesicles was not found. Rather, the primary result was the deterioration of tissue into a callus mass. Y. Gulsen et al., Physiologia Plantarum 53: 295-300 (1981) reported the formation in culture of atypical juice vesicles from the inner part of the explant (normal vesicle formation) and were normally situated on a stalk which arose from a cushion of callus.